The present invention relates to an automatic focusing apparatus used for optical instruments which are of variable focal length, such as a camera having interchangeable lenses.
There is known in the art a camera of the type having interchangeable lenses, namely, a wide angle lens and a telephoto lens arranged side by side. Such a camera allows photographers the flexibility of choosing a lens suitable for the object to be photographed.
On the other hand, there have been provided many types of automatic focusing apparatus, one being of the type having a lens which is automatically axially displaced in order to assume either of two fixed positions (which are referred to as lens positions) in accordance with the subject distance which is generally divided into two distance ranges, namely, a close range and a long range. Such a two-range automatic focusing apparatus, which facilitates ranging and lens adjusting, makes it easy to reduce the production cost of the camera. In the case where the above-mentioned two-range automatic focusing apparatus is incorporated into a camera of the type mentioned above, the distance ranges will be established in common to both lenses regardless of the focal lengths thereof. Therefore, when establishing the distance ranges and the lens positions so as to widen the limits within which one lens can be well focused, the limits within which the other can be well focused are unavoidably reduced. For example, when widening the limits in which a telephoto lens can be well focused, a wide angle lens which can be chosen in place of the telephoto lens exhibits worsened focusing conditions for close distances compared to the case in which there are provided the distance ranges and the lens positions peculiar to the telephoto lens. Therefore, it becomes impossible to improve focus conditions substantially, over a broad distance range.